Mystery £12.50 cap

Help, fare mathematicians. I thought I was a bit of an pro on these kinds of things but this has got me truly stumped.

I’m trying to work out why I got charged only £12.50 for a recent (August) weekday’s journeys, using contactless. I’ve had a bit of back-and-forth with TfL customer service emails over the last few weeks, and they simply say I’ve been charged the correct fare and offer me links to the regular webpages. I’ve tried various permutations and combinations of zonal caps, extension fares etc but can’t make anything fit the calculation.

My journeys were:
1. Morning peak-time tube+train journey from Northwood Hills tube (Zone 6) at 07:49 to East Croydon NR (Zone 5) arriving 09:07, touching out of the tube at London Bridge 08:38 and touching back in to the mainline station at 08:41 – £9.40 (which is what I expected as that’s what the single fare finder says)
2. Bus at 09:15 – £1.75
3. Bus at 09:45 – £0.00 (hopper) – actually the same service in the same direction.
4. Bus at 20:38 – £1.35 (“All Services Daily Cap”) – but I was expecting this to be a £1.75 second bus journey
5. Bus at 21:23 – £0.00 (hopper)
6. Bus at 22:02 – £0.00 (“All Services Daily Cap”) – I was expecting this to be a £1.75 third bus journey

So I thought I’d be hitting the bus+tram cap and, along with the morning journey, paying £14.65 for the day – just below the £14.90 Zones 1-6 daily cap. But instead it was £12.50 for the day.

I don’t use the network every day so was nowhere near a weekly cap for anything.